The present invention relates to a medical instrument for removing tissue in the human or animal body, having a tubular shaft that has at least one window in the region of its distal end, having a cutting element that is arranged in the shaft in the region of the window and is connected to a drive shaft, extending in the shaft, by way of which the cutting element can be driven rotationally about its longitudinal axis, the shaft having at least one bending point, and the drive shaft terminating proximally from the bending point and being connected to the cutting element through the bending point by way of at least one flexible element.
An instrument of this kind is known from U.S. Pat. No. 5,320,635. An instrument of this kind, which is also referred to as a rotary cutting instrument or a shaver, is used in minimally invasive surgery to remove tissue in the human or animal body. For that purpose, the distal end of the shaft is guided through an incision into the surgical area in which the tissue that is to be removed is located. For removal of the tissue, the cutting element is caused to rotate, via the drive shaft, by way of an external or internal motor. A blade configured on the cutting element coacts in cutting fashion, during rotation, with an edge of the window of the shaft also configured as a blade, by the fact that the blades of the cutting element pass by the blades on the window at each revolution.
In addition to instruments that have a continuous straight shaft, instruments of this type are also known whose shaft has a bending point in the region of the distal end, i.e. the shaft is curved in the region of its distal end. Because of the curved configuration of the shaft, it is possible to remove portions of tissue in the body that are inaccessible or difficult to access with a straight shaft. In orthopedics, for example, portions of tissue around joint structures can be removed therewith.
In the case of an instrument having a curved shaft, there arises the problem of transferring the rotation of the inherently rigid drive shaft, through the bending point or curvature of the shaft, to the cutting element; this is problematic because the longitudinal axis and thus the rotation axis of the cutting element, and the longitudinal axis and thus the rotation axis of the drive shaft, enclose an angle that differs from zero.
In the case of the instrument known from the aforementioned U.S. Pat. No. 5,320,635, the rotation transfer through the bending point is brought about in that the drive shaft, configured as a tubular shaft, is equipped, in the region arranged in the bending point, with circumferentially delimited indentations introduced perpendicular to the longitudinal axis in the manner of a bellows, thus making possible flexibility of the drive shaft in this region. Provision is also made for the drive shaft to be made of a flexible plastic at least in this region.
A disadvantage of this configuration, however, is that the slits introduced into the drive shaft can constitute defined break points, since as it rotates, the drive shaft is exposed in the bending region to continuously alternating bending directions. This configuration of the drive shaft, in particular in the case of a miniaturized configuration of the instrument with a thin shaft, is moreover complex in terms of manufacturing and cost, since the slits must be of very fine-scale configuration and suitable tools must be used for the purpose.
A further rotational cutting instrument is known from DE-A-43 23 756. With this instrument, the drive shaft is interrupted in the region of the bending point of the shaft, the respective adjacent ends of the rigid shaft parts being connected via one or more universal joints. The universal joints have two articulation axes orthogonal to one another.
This known type of rotation transfer from the drive shaft to the cutting element again results in a complex design for the instrument. With miniaturized configurations of the instrument in particular, the universal joints must also be of miniaturized configuration. The manufacture of such miniaturized universal joints is, however, laborious.
Also known, from U.S. Pat. No. 5,669,926, is a rotary cutting instrument in which the drive shaft is connected to the cutting element, through a bending point of the tubular shaft, via a flexible coil, the coil having the same diameter as the drive shaft. This type of rotation transfer through a bending point is also associated with increased outlay for manufacture of the drive shaft.
DE 43 02 912 A1 discloses a rotary cutting instrument in which the drive shaft is constructed of gimbal elements in a curvature region of the tubular shaft.
A similar configuration of the drive shaft in the region of a bend in the tubular shaft, by arranging gimbal elements one behind another and in mutual engagement, is known from U.S. Pat. No. 5,755,731.
A drive shaft similar to the configuration of the drive shaft described in the aforementioned U.S. Pat. No. 5,320,635 is known in the case of a rotary cutting instrument disclosed in U.S. Pat. No. 5,620,447.
Lastly, U.S. Pat. No. 5,529,580 discloses a rotary cutting instrument in which the rotation transfer from the drive shaft through a bend in the tubular shaft to the cutting element is accomplished by an element similar to a helical spring.
All the aforementioned known types of flexible configuration of the drive shaft in the region of the bend in the shaft have the disadvantage of being complex in terms of design and production engineering.
It is therefore the object of the invention to develop an instrument of the kind cited initially in such a way that rotation transfer from the drive shaft to the cutting element through the at least one bending point is made possible with little complexity in terms of design.